The Size, Structure, and Variability of Late-Type Stars Measured ...

More documents

Recommendations

Info

11 1.4 Stellar Evolution and AGB Stars Late-type AGB stars are ideally suited for observation with the ISI. These stars are nearing the end of their lives, and have grown to several hundred times their original size. Extremely luminous, they have relatively cool temperatures on the order of 3000 K. Because of their mostly infrared flux and their relatively large angular size, the ISI is able to obtain accurate visibilities on a number of these stars. The following section discusses the stellar life cycle and, in particular, the workings of AGB stars like the ones considered within this thesis. It is included to serve as a background for those unfamiliar with stellar structure and evolution and to provide a framework of how AGB stars, including the Mira variables and supergiants discussed within this thesis, fit into stellar populations. Most of the information pertaining to stellar evolution comes from Prialnik (2000) [78] and Padmanabhan (2001) [74]. A star, by definition, is a gravitationally bound object radiating due to an internal source. Typically, stars are spherical because gravity acts in a radially symmetric way, and their energy source is nuclear fusion occuring in the core. However, energy released from gravitational self-attraction or stored in the heat capacity of its matter is not necessarily negligible for stellar phenomenon which occur over time scales characteristic of these processes. Although elemental composition does vary between stars, the total stellar mass is the defining parameter for a star. It determines the size, structure, lifetime, and evolutionary course a star will have. The Hertzsprung-Russell (H-R) diagram is a plot of the surface temperature vs. luminosity for a collection of stars. Individual stars are points in the plane and variations occur in two dimensions due to the one-parameter variations in both mass and age. Patterns do exist in the H-R diagram, and the populations and evolutionary tracks of stars within it can be reproduced quite well from theoretical predictions. Figure 1.5 shows an H-R diagram of almost 9000 stars from Perryman et al. (1995) [77]. The ordinate of the plot is B-V magnitude instead of temperature although these quantities are directly related for the most part. Only stars whose parallax was measured with precision better than 10% were plotted. Hence, the collection is not necessarily a representative pool of all stars. A long band of stars known as the main sequence is seen to contain most stars. These stars are in the longest portion of their life-cycle and vary in mass from about 0.1 M ⊙ at the bottom-right corner, to 10 M ⊙ in the upper-left. Another grouping of stars occurs at higher luminosities and cooler temperatures in the top-right portion of the diagram. These are
1995A&A...304...69P 12 Figure 1.5: Hertzsprung-Russell Diagram of ∼9000 Stars from Perryman et al. (1995) [77]. The main-sequence band of stars is the dominant shape stretching from high-mass stars in the top-left to low-mass stars in the lower-right. These stars are in the longest stage of their evolution. Late-type stars are found above and to the right of the main-sequence. A handful of white dwarf stars can be seen in the extreme lower left corner of the plot.
Page 1 and 2: The Size, Structure, and Variabilit
Page 3 and 4: 1 Abstract The Size, Structure, and
Page 5 and 6: iv 5 Spectroscopy and ISI Measureme
Page 7 and 8: vi 3.15 Density, Temperature, and C
Page 9 and 10: viii Acknowledgements Over the cour
Page 11 and 12: 2 to achieve resolution characteris
Page 13 and 14: 4 sources are not coaligned perfect
Page 15 and 16: 6 Intensity Profile Hankel Transfor
Page 17 and 18: 8 Figure 1.3: Possible Effective Ba
Page 19: 10 6LJQDO'HWHFWRU 6LJQDO'HWHFWRU /D
Page 23 and 24: Figure 1.6: Stellar Evolution of a
Page 25 and 26: 16 such as Mira variables, become u
Page 27 and 28: 18 wavelengths, however, its range
Page 29 and 30: 20 Figure 2.1: ISI Data for o Cet f
Page 31 and 32: 22 Figure 2.3: Uniform Disk, Limb D
Page 33 and 34: 24 2.2 Comparison of ISI Data with
Page 35 and 36: 26 Table 2.3: Diameter Measurements
Page 37 and 38: 28 measurements. χ Cyg and R Leo a
Page 39 and 40: 30 metric flux (from the reference
Page 41 and 42: 32 their surface. Very often, mater
Page 43 and 44: 34 Mira. Finally, variations in tim
Page 45 and 46: 36
Page 47 and 48: 38 Figure 3.2: Intensity Distributi
Page 49 and 50: 40 Figure 3.4: Ratio of the Best-Fi
Page 51 and 52: Figure 3.5: Synthetic Near-Infrared
Page 53 and 54: 44 Angular Diameter (mas) 60 50 40
Page 55 and 56: 46 wavelengths which would cause th
Page 57 and 58: 48 3.4.1 Static Radiative Transfer
Page 59 and 60: 50 Figure 3.8: Ratio of Photospheri
Page 61 and 62: 52 3.4.2 The Effect of Dynamic Phen
Page 63 and 64: 54 Figure 3.10: “Standard” Bowe
Page 65 and 66: 56 extension is reflected at wavele
Page 67 and 68: 58 photosphere. These results suppo
Page 69 and 70: 60 Figure 3.13: Continuum Opacity o
Page 71 and 72:
62 assuming only continuum sources.
Page 73 and 74:
64 Figure 3.16: Normalized Syntheti
Page 75 and 76:
Figure 3.17: Density and Temperatur
Page 77 and 78:
68 Figure 3.19: Apparent Size of H
Page 79 and 80:
70 of Fox and Wood (1985) [31] are
Page 81 and 82:
72 3.5 Explanation of Variations in
Page 83 and 84:
74 Figure 3.21: 2.1 µm Image of 25
Page 85 and 86:
76 at visible wavelengths either by
Page 87 and 88:
78 4.1 Implications of Diameter Mea
Page 89 and 90:
80 11 µm Diameter of o Cet vs. Dat
Page 91 and 92:
82 Figure 4.3: A uniform intensity
Page 93 and 94:
84 phase observed in the continuum
Page 95 and 96:
86 5.1 General Results of 11 µm Sp
Page 97 and 98:
88 depth are the contours plotted a
Page 99 and 100:
90 Figure 5.3: Best Fitting Calcula
Page 101 and 102:
92 of its three parameters. The con
Page 103 and 104:
94 H 2 O on their measured diameter
Page 105 and 106:
96 5.3 Modelling Spectral Features
Page 107 and 108:
98 Figure 5.7: Stellar Intensity Pr
Page 109 and 110:
Figure 5.9: Observed H 2 O Spectral
Page 111 and 112:
Figure 5.10: Höfner Model Predicte
Page 113 and 114:
104 30 km/s causes the spectrum to
Page 115 and 116:
Figure 5.13: o Cet Spectra in Obser
Page 117 and 118:
108 density prediction matches the
Page 119 and 120:
110 Dixon. The infrared angular dia
Page 121 and 122:
112 [29] M. U. Feuchtinger, E. A. D
Page 123 and 124:
114 [50] A. P. Jacob, T. R. Bedding
Page 125 and 126:
116 [70] A. A. Michelson and F. G.
Page 127 and 128:
118 [92] Martin Schwarzschild. Over
Page 129:
120 [114] P. Woitke, D. Krüger, an
show all

The Size, Structure, and Variability of Late-Type Stars Measured ...

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?